BIRD-LIKE GROUP. 
37 
OUTER AND LATERAL VIEWS OF A TOOTH OF 
THE IGUANODON. 
bar of the pubis is inclined backwards, parallel to the ischium, while it has 
a secondary plate projecting forwards. In this parallelism of the pubis and 
ischium these dinosaurs resemble birds (see the figure inVol. III. p. 290), and birds 
alone; and from this and other features it is pretty certain that the latter are 
derived from reptiles more or less closely allied to this or the preceding group of 
dinosaurs; the resemblance in the one case being closest in the structure of the 
pelvis, and in the other of the hind-limb. All the bird-like dinosaurs are further 
characterised by the presence of a separate chin-bone {pel in the figure on p. 3) 
at the extremity of the lower jaw; by the 
absence of teeth from the front of both 
jaws; by the teeth themselves approximat¬ 
ing more or less closely to the type of the 
one here represented, and by being fre¬ 
quently not implanted in distinct sockets; 
and likewise by the vertebrae being com¬ 
pletely solid throughout. The typical 
representatives of this group are the well- 
known iguanodons, originally described on 
the evidence of teeth, from the Wealden 
rocks of England, but now known by 
entire skeletons from the corresponding- 
deposits of Belgium, which are exhibited in 
the museum at Brussels. These reptiles, 
which were represented by allied forms in the United States, habitually walked 
on their three-toed hind-limbs, the largest individuals attaining a length of some 
33 feet. They are characterised by the limb-bones being hollow, by the length 
of the metatarsal bones of the foot, by the first digit of the five-toed fore-limb 
being converted into a large conical spine, and also by the teeth being of the type 
of the one shown in the accompanying figure. Needless to say, animals with 
such teeth must have been purely vegetable 
feeders, as indeed were all the other members 
of this group. The hind - feet terminated in 
rather sharp claws, and there was no bony 
armour on the body. The iguanodons probably 
stalked about among the palm-forests of the 
Wealden period, on the leaves and fruit of 
which they may be presumed to have in great 
part subsisted. In these reptiles the large 
flattened and serrated teeth were arranged in each jaw in a single row, but in cer¬ 
tain smaller forms known as tracliodons, 
which occur in the higher Cretaceous 
rocks of both Europe and North America, 
there were several rows of teeth in use 
at the same time, the edges of these 
teeth beino; so flattened and fitted to- 
° TERMINAL TOE-BONE OF AN ARMOURED 
gether that a pavement-like structure dinosaur.— After Marsh. 
PAVEMENT-LIKE TEETH OF THE TRACHODON.— 
After Marsh. 
